1. Field of the Invention
The present invention relates to a wire guide or stylet assembly for the introduction of medical catheters or electrical leads to a desired site within a patient's body, and specifically to a steerable stylet assembly for imparting a desired dynamic curvature in the distal portion of a catheter or lead during its introduction in order to guide it through curvature in the patient's vascular system and to a desired site in the patient's cardiovascular system.
2. Description of the Prior Art
The marked advances in cardiac and vascular surgery in the past few years and other medical problems that require diagnostic study of the vascular beds and systems as well as the advances in pacing and cardioversion, has led to the extensive use of cardiac or vascular catheters, such as percutaneous transluminal coronary angioplasty (PTCA) catheters and transvenous or endocardial pacing and cardioversion leads. The insertion of a relatively long catheter or lead body to an internal site requires advancement of the catheter or lead into branch vessels at varying angles relative to the feeding direction of the catheter or a lead.
In respect to the introduction of PTCA catheters, for example, several techniques for introducing such catheters are available, including the cut-down method and the Seldinger techniques. The Seldinger technique involves puncturing a vein or artery with a needle, inserting a guide wire into the vein or artery through the lumen of the needle, withdrawing the needle, inserting over the guide wire a dilator located inside a sheath, removing the dilator and inserting a catheter or lead through the sheath into the blood vessel. In this procedure, flexible spring guide wires, of the type disclosed in commonly assigned U.S. Pat. No. 4,815,478 to Buchbinder, et al, and the numerous patents referenced therein, are steered to the desired internal site by remotely deflecting the tip of the guide wire to facilitate movement of the guide wire around or through a curved path in the blood vessel. The steerable spring guide wire of the '478 patent possesses a flexible tip constructed with flexible spring coil wire extending from a flexible elongated tubular body and coupled to a long tip which is additionally coupled to a deflection wire extending through the flexible tubular body and the spring coil as well as a control wire extending through the lumen to provide for the deflection of the distal tip portion by the application of traction to the proximal end of the control wire. The control wire remains within the confines of the tubular body as well as the loosely-wound flexible spring coil distal portion thereof. As stated above, once the distal portion of the guide wire is advanced to the desired internal site, then the lumen of the tubular catheter is advanced over the guide wire until its distal tip is advanced to the desired internal site, whereupon the guide wire is withdrawn.
In the pacing and cardioversion context, it is well known to guide the insertion and proper placement of an endocardial lead to a desired internal site in a chamber of the patient's heart or in a vessel, such as the coronary sinus, through the use of a stiffening stylet inserted into the lumen of the pacing or cardioversion lead. Generally speaking, it is highly desirable that pacing and cardioversion leads be so flexible through their length that they are capable of flexing with the movement of the heart and other muscular movement so as to avoid the fracture of the lead body due to its cumulative stressing. Thus, implantable pacing and cardioversion leads are often too limp to be advanced on their own through the venus system to the desired internal site and it has been commonplace for many years to employ thin wire stylets extended down the lumen of the lead to stiffen the entire assembly and to impart a desired degree of curvature of the tip of the lead body during insertion. To accomplish this desirable result, the solid inner stylet wire is given a bend or curvature near its distal end by the physician when it is outside the lumen. After insertion through the lumen, the curved distal portion facilitates movement of the distal tip of the lead through blood vessels into chambers as the lead is advanced and thereafter assists in directing the lead tip to the desired internal site within the patient's heart or cardiovascular system.
It is also commonly known to employ a stylet to straighten an atrial pacing lead, which is provided with a permanent "J"-shaped bend to facilitate both the positioning and the retention of the atrial electrode in the patient's atrial appendage as taught, for example, in U.S. Pat. No. 4,136,703, to Wittkampf. Insertion of these "J"-shaped leads is greatly facilitated through the use of a straight solid inner stylet which, in this case, straightens the bend normally fixed within the distal end of the lead itself.
Such transvenous pacing and cardioversion leads typically comprise a length of coiled wire conductor formed around an axial lumen and encased within a suitable insulating material, such as silicone rubber or polyurethane, that is substantially biocompatible and stable to body fluids and tissues. A hollow connector pin is attached coaxially into the lumen and electrically to the proximal end of the conductor. An electrically conductive electrode at the distal end of the conductor is adapted to be placed in contact with the endocardium or within the coronary sinus of the patient. Generally, when more than one length of separately-insulated coiled wire conductors are employed in modern pacing and cardioversion leads, each coiled wire conductor is wound coaxially around the centrally-disposed lumen which extends through the connector pin and the corresponding lengths of coiled wire conductors to the distal end of the lead body. The lumen receives the stiffening stylet, typically a cylindrical wire, for imparting stiffness and curvature to the distal portion of the lead body to facilitate its advancement through the venous system and to the desired internal site. Further details of the construction and utility of such endocardial pacing leads may be obtained by reference to U.S. Pat. Nos. 4,506,680 and 4,577,642 to Stokes; 4,606,118 to Cannon et al; and 4,711,281 to Kessel et al. each incorporated herein by reference.
Insertion of such endocardial pacing and cardioversion leads frequently requires the physician to commence the introduction through a lead introducer inserted into a vein through a skin puncture. At the outset, the stylet may be straight or curved to facilitate the introduction into the vein and through the initial curvature thereof. Thereafter, and from time to time, as the physician directs the distal tip of the lead to the desired location, it may be necessary to withdraw the stylet and substitute a new stylet having a different curvature, reinsert it, and advance the distal portion of the lead a bit further until another obstacle to advancement is encountered.
This technique, however, has several drawbacks. For example, repeated insertion and withdrawal of the stylet may contaminate the lumen with blood. This is undesirable because drying blood can jam the stylet within the pacing lead, making stylet removal difficult and possibly rendering the lead unusable. Moreover, the continual insertion and withdrawal of stylets is time consuming and offers the potential of damaging the lead or blood vessel or both in the process.
In order to avoid repeated withdrawal and reintroduction of stylets, various approaches have been proposed including those disclosed in commonly assigned U.S. Pat. No. 4,381,013 to Dutcher and U.S. Pat. No. 4,677,990 to Neubauer. The '013 patent discloses use of a two-piece stylet having an inner solid portion for enabling a shape to be imparted to the lead to facilitate introduction in the fashion as described above and an outer tubular portion which enables the transmission of torque applied by the physician at the proximal end of the stylet to be transmitted to a helical fixation means located at the distal end of the lead. The transmission of this torque allows the helical fixation means to be screwed into the endocardial tissue. Thus the inner solid wire stylet operates in the same fashion as the conventional solid wire stylets described above.
The '990 patent discloses the combination of a removable stylet stiffening wire and one or more threads having very low elasticity which are coupled near the distal end of the lead or at selective locations along the lead body extending for a portion of the length of the lead within the lead lumen and for a further portion outside the lumen but within the outer insulative sheath. With the stylet inserted, traction applied to the proximal portion of the thread or threads imparts a curvature into the lead body as the thread is pulled taut. The curvature is dictated by the locations at which the thread or threads are directed in the space between the outer insulative sheath and the coiled wire conductor. To achieve easier bending, the stylet is described as having portions of reduced thickness along its length in parallel with the location of the threads passage outside the lumen.
The '990 patent addresses concerns raised by the conventional technique of withdrawing, imparting a new curve, and reinserting the stiffening stylet during the implantation procedure.
The use of the separate thread and stylet in the '990 patent and the two-piece stylet of the '013 patent, as well as the conventional one-piece stylets, usually require the physician to employ both hands in manipulating the lead and stylet to advance and withdraw the stylet and rotate the lead body in manipulating the advancement of the distal portion of the lead through the venus system or into particular desired sites for lodging the electrodes. U.S. Pat. No. 3,452,740 to Mueller discloses a spring guide manipulator for imparting a curvature and rotation in a spring guide by one-handed use of a manipulative handle. The spring guide wire includes the conventional inner straight wire coupled to the distal end of the coiled wire of the distal portion of the spring wire guide. When the handle is attached to a guide wire and a catheter is fitted over the guide wire, it is reported that the handle may be employed to both rotate the guide wire and catheter as well as place a curve in the distal portion of the catheter.
A further example of a steerable device is disclosed in U.S. Pat. No. 4,846,175 to Frimberger. That patent discloses a steerable probe which, in one embodiment, has an elongated, flattened cross-section and a pull wire exposed to the exterior between two openings. The '175 devices further uses the exposed pull wire to electrically cut tissue, such as a gallstone.
Despite these devices, a need remains for a simple and reliable easy-to-use steerable stylet or catheter guide wire assembly which provides a wide degree of dynamic curvature to the lead or catheter being advanced by the physician.